Weight regulations limiting the loaded weights of commercial vehicles are almost universally in effect. These regulations generally specify the maximum load of each vehicle axle as well as the maximum total load. Fines are usually levied against operators who are found violating these regulations. To maximize profits, vehicle operators normally load their vehicles as close as possible to the legal load limit. In order to do this, the vehicle operator must be able to accurately measure the vehicle's weight while the vehicle is being loaded.
On-board vehicle weighing systems have been developed to accurately measure the vehicle's weight, including while the vehicle is being loaded. In these on-board weighing systems, strain gauge-based sensors are generally secured to structural members of the vehicle, usually the axles. However, conventional strain gauges placed on tandem axles to measure loading experienced significant accuracy problems.
Other on-board load measuring systems utilize load cells placed on structural members between the axles and the load. However, these systems also have shortcomings. While these systems can be highly accurate, they typically are more expensive. In addition, they are difficult to retrofit on existing vehicles and cannot sense the extra weight added to a vehicle by dirt and other debris collected on the surfaces of the vehicle suspension beneath the load cells.
Other on-board load measuring systems measure the relative displacement of the springs or the relative displacement between the vehicle frame and axle. However, the accuracy of these devices is adversely affected by wear, friction and debris.